1. Field of the Invention
The present invention relates to a screw compressor for increasing the pressure of a gas, vapor or mixture of the gases and vapors, and more particularly a compressor casing for accomodating a pair of intermeshing rotors or screws.
2. Description of the Prior Art
There is one known compressor generally comprising a casing defining therein a pair of cylindrical chambers axially intersected with each other, and a pair of male and female screws rotatably mounted in the respective chambers for counterrotation in an intermeshing relation with each other. A typical compressor of this type is illustrated in FIGS. 7 and 8. The casing includes a rotor casing body 1 having therein the cylindrical chambers or space, an inlet casing 6 having therein an inlet port 21, and an exit or delivery casing 3 providing an exit port 32, in cooperation with the casing body 1. The inlet and exit ports 61,32 are disposed at axially opposite ends of the chambers 14,15, respectively, the two ports being in communication with the latter. The inlet and exit casings 6,3 have respective end surface 63,30 extending perpendicularly with respect to the parallel axes of the chambers 14,15 at the opposite ends, respectively. The inlet casing 2 includes a pair of parallel tubular walls 62 and an end wall partitioning partially the inlet port 61 extending around the tubular walls 62 apart from the chambers. The end wall has a closure end surface 9 serving to close the chambers 14,15 at one ends thereof. The exit casing 3 has an end surface 30 serving to close the chambers at the other ends thereof. The exit port 32 extends from a corner portion of the chambers 14,15 outwardly with a cross-sectional area which progressively increases. The male and female screws 4,5 have shafts 40, 50 extending coaxially with respect to the respective axes of the chambers and rotatably received in the inlet and exit casings 2,3. The two shafts are operatively coupled to drive means (not shown) for rotation via gearings and other coupling means (not shown). The male screw 4 has a plurality of helical lobes or teeth 41 and helical tooth grooves 41a extending in parallel along the axis thereof, while the female screw 5 has a plurality of helical grooves 51 extending along the axis thereof, the respective teeth intermeshing with the respective corresponding grooves in an axial space extending along an intermediate vertical plane in which the chambers 14,15 are intersected.
In operation the two screws counterrotate in a constant intermeshing engagement relationship with each other. The gas is sucked or rammed axially into the chambers 14,15 through the inlet port and enclosed or trapped within the chambers in the tooth grooves and the grooves. The compressed gas is then discharged or delivered from the chambers through the exit port 3 in a known manner. In such an axial flow compressor having the inlet port 61 disposed axially upstream of the chambers 14, 15, the gas generally yields an inertia supercharge effect when it is sucked axially into the gas chambers, with the result that the gas specific suction volume becomes greater than the actual gas suction volume. The prior compressor, however, has a drawback in that the end surface 63 extends over a position in which the inertia supercharge effect occurs. This arrangement tends to hinder the inertia inward flow of the gas, thus impairing such an advantageous effect. The hindered gas causes a tubulent flow of the gas in the inlet port 61, which leads to greater loss of energy during the suction process. Such a known inlet casing has the end surface 63 which makes the construction of the inlet casing become objectionably complicated, thus requiring elongated time and tedious work for manufacturing it.